1. Technical Field
The present invention relates to a liquid crystal display apparatus included in a television receiver, a personal computer or the like.
2. Description of Related Art
Among display apparatuses, a liquid crystal display apparatus is a thin type display and has characteristics such as low power consumption. A display panel of the liquid crystal display apparatus has a color filter (CF) substrate, a liquid layer, an active matrix substrate (TFT substrate), and two polarizing plates. The CF substrate and the active matrix substrate are bonded to each other with a seal material interposed between them, and liquid crystal is injected between them to form a liquid crystal layer. The active matrix substrate has a pixel electrode on the liquid crystal layer side, and the CF substrate has a common electrode on the liquid crystal layer side. The two polarizing plates are disposed on a surface opposite to the liquid crystal layer side of each of the CF substrate and the active matrix substrate.
The liquid crystal display apparatus using a vertical alignment type material as a liquid crystal material is called a vertical alignment (VA) mode liquid crystal display apparatus. The liquid crystal display apparatus, in order to improve transmittance and response speed thereof, employs an alignment division structure in which a plurality of liquid crystal domains are formed in one pixel. As a method of forming the alignment division structure, there may be a multi-domain vertical alignment mode (MVA). In the MVA mode, an alignment regulation structure is obtained by providing a linear projection on the liquid crystal layer side of the substrate which sandwiches the liquid crystal layer, and providing an opening part (slit) on the pixel electrode. By the alignment regulation structure, a plurality of liquid crystal domains are formed in the pixel (for example, Japanese Patent Laid-open Publication No. 2003-149647). By finely forming the slit, an alignment of the liquid crystal molecules may be more controlled, and the transmittance of light and response speed may be improved.
The VA mode, which is configured in such a manner that alignment films such as a photo alignment film are respectively provided on the liquid crystal layer sides of both substrates facing each other with the liquid crystal layer interposed between them so that pre-tilt directions (alignment treatment directions) are orthogonal to each other, and the liquid crystal molecules have a twist alignment during applying a voltage thereto, is called a vertical alignment twisted nematic (VATN) (for example, International Publication No. 2006/132369). Among them, a structure, in which four liquid crystal domains which are divided into two rows and two columns during applying a voltage thereto are formed in one pixel region, by regulating the pre-tilt directions using the two alignment films, is called a 4D structure.
FIG. 19 is a plan view illustrating a pixel region of the VATN mode liquid crystal display apparatus having the 4D structure.
In FIG. 19, dotted line arrows illustrate pre-tilt directions which are regulated by the photo alignment film provided on the active matrix substrate, and solid line arrows illustrate pre-tilt directions which are regulated by the photo alignment film provided on the CF substrate. In addition, tilt direction (standard alignment direction) of each liquid crystal domain when a voltage is applied to the liquid crystal layer is illustrated by a direction of pins. FIG. 19 illustrates that the liquid crystal molecules are tilted so that a circular plate part of the pin is close to a viewer who views the liquid crystal display apparatus. That is, the standard alignment direction is oblique 45°.
The pixel electrode of the liquid crystal display apparatus has no slit formed therein.
FIG. 20 is a plan view illustrating a light transmission state of a pixel region in FIG. 19, and FIG. 21 is a plan view illustrating the light transmission state of the pixel region when a wiring and a contact hole are disposed.
From FIGS. 20 and 21, it can be seen that dark lines having a wide width are generated a boundary portion of the liquid crystal domain. The dark lines are generated due to the liquid crystal molecules being aligned in a direction vertical or parallel to a polarizing axis (longitudinal direction and lateral direction axes) at the boundary portion of the liquid crystal domain, and thereby light is not transmitted therethrough.
The transmittance of light is decreased by the dark lines. Particularly, in a high definition display having a small pixel, the effect of a decrease in transmittance of light by the dark lines becomes larger.
Assembling the above-described MVA mode in the VATN mode having the 4D structure has also been attempted (multi-domain VATN mode, for example, International Publication No. 2013/054828 and the like).
FIG. 22 is a plan view illustrating a pixel electrode 52 of the active matrix substrate in the pixel region of a multi-domain VATN mode liquid crystal display apparatus.
In the pixel electrode 52, a plurality of oblique slits 21 are formed by matching with each tilt direction of the oblique 45° of four liquid crystal domains. By the oblique slits 21, the above-described dark lines generated at the boundary portion of the VATN mode liquid crystal domain are reduced, and thus the transmittance of light may be increased. A contact hole 12 is formed in a center part of the pixel region.
FIG. 23 is a plan view illustrating the light transmission state of the pixel region in FIG. 22, and FIG. 24 is a plan view illustrating the light transmission state of the pixel region when the wiring and the contact hole are disposed.
Also in this structure, it can be seen that dark lines having a constant width are formed at the boundary portion, and a sufficient effect may not be obtained. In addition, the dark lines along the oblique slits 21 are also generated.
FIG. 25 is a partial enlarged view of FIG. 24.
In FIG. 25, the alignment of the liquid crystal molecules is illustrated by pins.
As illustrated in FIG. 25, most of liquid crystal molecules 61 are aligned vertical to a polarizing axis at the boundary portion, while some liquid crystal molecules 61 are aligned substantially parallel to the polarizing axis, and a portion having a constant width in which light is not transmitted is generated, and thereby the transmittance of light is decreased.
FIG. 26 is a plan view illustrating the pixel electrode 52 of the active matrix substrate in the pixel region of another liquid crystal display apparatus.
The pixel electrode 52 is provided with slits 28 and 28, and slits 29 and 29, in addition to the plurality of oblique slits 21. The slit 28 is formed by connecting each polarizing axis side end part of three oblique slits to a slit parallel to a longitudinal polarizing axis. The slit 29 is formed by connecting each polarizing axis side end part of two oblique slits to a slit parallel to a lateral polarizing axis.
FIG. 27 is a plan view illustrating the light transmission state of the pixel region in FIG. 26.
As illustrated in FIG. 27, it can be seen that the dark lines having a wide width are generated in a portion in which the polarizing axis side end parts of the oblique slits are connected to the slit parallel to each polarizing axis.